Wake up device for a communications system

ABSTRACT

The present invention teaches a communications system comprising a first communications device for receiving data and a wake up signal. The first communications device comprises an active mode of operation and a sleep mode of operation for reducing power consumption. Further, the system comprises means for switching the first communications device to and from sleep mode in response to receiving the wake up signal. Further, the system comprises a second communications device for transmitting data to the first device during its active mode, while transmitting the wake up signal to the first device during its sleep mode.

FIELD OF THE INVENTION

[0001] The present invention relates to a communication systems. More particularly, the invention pertains to a multi-mode communications system.

BACKGROUND OF THE INVENTION

[0002] Recently, there has been increased research and development with respect to Radio Frequency Identification (“RFID”) device tags. These RFID tags essentially comprise small radio transceivers attached to a movable object. By coupling an RFID tag to an object, it has been intent of developers of creating a system for tracking the whereabouts and identification of the object.

[0003] Several RFID systems have been developed. Generally, these designs have been relatively large in size—approximately cigarette package—and have been generally fabricated using hybrid circuit techniques. Besides their bulky size, the systems require the RFID tag to constantly remain activated.

[0004] Recently, there have been several breakthroughs in techniques in the design and manufacture of RFID tags. Examples of these include “Radio Frequency Identification Device (RFID) and Method of Manufacture, Including an Electrical Operating System and Method,” U.S. patent application Ser. No. 899,777, filed on Jun. 17, 1992, “Anti-Theft Method for Detecting The Unauthorized Opening of Containers and Baggage,” U.S. patent application Ser. No. 921,037, Jul. 24, 1992, “Electrically Powered Postage Stamp or Mailing or Shipping Label Operative with Radio Frequency (RF) Communications,” U.S. patent application Ser. No. 928,899, filed on Aug. 12, 1992, and “Modulated Spread Spectrum in RF Identification Systems Method,” U.S. patent application Ser. No. 032,384, filed on Mar. 17, 1993, all commonly assigned to Micron Semiconductor, Incorporated, and all incorporated herein by reference.

[0005] It has been thus a design criteria that these RFID tags be light weight and inexpensive. However, these systems previously have not addressed the need of low power consumption. Presently, RFID tags must be active to detect their location, as well as additional information. As such, there is a need to develop a RFID tag communications system having an active mode for receiving/transmitting data and a sleep mode for reducing power consumption.

SUMMARY OF THE INVENTION

[0006] In order to achieve the benefits of the present invention, a system is disclosed comprising a first communications device for receiving data and a wake up signal. The first communications device comprises an active mode of operation and a sleep mode of operation for reducing power consumption. Further, the system comprises means for switching the first communications device to and from sleep mode in response to receiving the wake up signal. Further, the system comprises a second communications device for transmitting data to the first device during its active mode, while transmitting the wake up signal to the first device during its sleep mode.

[0007] Moreover, a method is disclosed for reducing the consumption of energy in operating a communications system. The communications system comprises a transmitter, a master receiver and a wake up receiver. The master receiver has at least an active mode and a sleep mode of operation and the wake up receiver using substantially less power than the master receiver. Initially, data is transmitted to and received by the master receiver during its active mode, while a wake up signal is transmitted and received by the wake up receiver during the master receiver's sleep mode. It should be noted that the wake up signal comprises a predetermined frequency and a predetermined rate of data transmission. Subsequently, the predetermined frequency and a predetermined rate of data transmission signal are detected. Upon detecting both, the master receiver is enabled for receiving data system in response to detecting the wake up signal.

[0008] The objects and advantages of the present invention will become apparent to those skilled in the art from the following detailed description read in conjunction with the appended claims and the drawings attached hereto.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The present invention will be better understood from reading the following description of non-limitative embodiments, with reference to the attached drawings, wherein below:

[0010]FIG. 1 is an high level architecture of the present invention;

[0011]FIG. 2 is a flow chart illustrating the method of the present invention;

[0012]FIG. 3 illustrates a first embodiment of the present invention; and

[0013]FIG. 4 illustrates a second embodiment of the present invention.

[0014] It should be emphasized that the drawings of the instant application are not to scale but are merely schematic representations and are not intended to portray the specific parameters or the structural details of the invention, which can be determined by one of skill in the art by examination of the information herein.

DETAILED DESCRIPTION OF THE INVENTION

[0015] Referring to FIG. 1, a wake up device for a communications system is illustrated. As shown, the system comprises a first and second communications devices; a transmitter 10 and a receiver 12. Transmitter 10 is coupled to antenna 5 in order to properly transmit data and a wake up signal to receiver 12. Receiver 12 comprises a wake up receiver 20 and a master receiver 25, which are both coupled to antenna 15. Further, receiver 12 comprises a switch, which enables the substantial energy savings. It should be noted that the issue of energy saving with respect to transmitter 10 is not important as it is not coupled to an RFID tag, unlike is receiver 12 in the preferred embodiment.

[0016] To accomplish these energy savings, master receiver 25 comprises at least two modes of operation. In the preferred embodiment, the first mode is referred to as an active mode of operation and the second mode referred to as a sleep mode. Further, wake up receiver 20 requires substantially less power for its operation than master receiver 25.

[0017] In the active mode of operations, master receiver 25 functions as a traditional receiver, capable of receiving data transmitted by transmitter 10. By contrast, in order to reduce power consumption during periods of inactivity, master receiver 25 comprises a sleep mode. During sleep mode, master receiver 25 utilizes a minimal amount of energy for biasing purposes. Thus, by utilizing this design scheme, a substantial power savings from receiver 12 can be achieved, which directly corresponds to the life expectancy of battery powered receiver 12. For example, in one receiver design, a 98% power savings has been observed.

[0018] Coupled between master receiver 25 and wake up receiver 20, is switch 30. Switch 30 switches master receiver 25 between its mode of operation—ie., active to sleep mode, as well as sleep mode to active mode—in response to the arrival of a wake up signal. As such, transmitter 10 transmits a wake up signal to receiver 12, which is ultimately received by wake up receiver 20. Upon detecting the wake up signal, a mode change signal is generated to switch 30. Accordingly, switch 30 changes the mode of operation of master receiver.

[0019] In the preferred embodiment of the present invention, switch 30 only switches master receiver 25 from sleep mode to active mode. Here, upon receiving wake up signal, wake up receiver 20 generates a mode change signal to switch 30. In response, switch 30 senses the mode of operation of master receiver 25. Thus, switch 30 switches master receiver to active mode upon sensing master receiver 25 as being in sleep mode. Contrarily, switch 30 is inactive upon sensing master receiver 25 as being in an active mode of operation. In this embodiment, master receiver 25 further comprises a timing scheme which switches master receiver from active mode to sleep mode. This timing scheme is enabled when a predetermined period passes in master receiver 25 without receiving any data from transmitter 10. The length of the period is dependent on several design criteria including the system's application and environment, as well as the desired probabilities of error. In a further embodiment of the present invention, switch 30, low power receiver 20 and master receiver 25 are all positioned on a radio frequency identification (“RFID”) tag.

[0020] Referring to FIG. 2, a flow chart illustrating the method for reducing the consumption of energy in operating a communications system of the present invention employing the architecture described herein. Initially, a wake up signal is transmitted by transmitter 10, and subsequently, the wake up signal is detected by wake up receiver 20. Finally, the mode of operation of the master receiver 25 is changed in response to the detection of the wake up signal.

[0021] In one embodiment of the present invention, the step of detecting the wake up signal, itself, comprises a series of steps. First, a predetermined frequency is detected from the wake up signal. In the event that that frequency is found, a predetermined data rate is detected from the wake up signal. If that frequency is not found, master receiver 25 is kept asleep. In the event that data rate of transmission of a certain number of bits per second is found, an output signal is generated. If that data rate of transmission is not found, master receiver 25 is kept asleep. This step of generating an output signal further comprises the step of comparing the output signal with a reference voltage. By doing so, switch 30 is enabled upon detecting a predetermined frequency and a predetermined data rate of transmission and master receiver 25 is woken.

[0022] Referring to FIG. 3, a first embodiment of the present invention is depicted. In order to receive a wake up signal, an antenna 50 is coupled with a frequency detector, realized by a first bandpass filter 55 having a bandwidth and a radio frequency (“RF”) output. First bandpass filter 55, operating in tandem with antenna 59, detects the frequency of the wake up signal. To avert the detection of noise as a wake up signal, the bandwidth of first bandpass filter 55 is substantially narrow. Nonetheless, in the preferred embodiment, first bandpass filter 55 must detect a predetermined frequency and a related harmonic.

[0023] While the present invention utilizes a narrow bandpass scheme for frequency detection, it should be obvious to one of ordinary skill in the art that the frequency detector can be realized using alternate hardware. For example, in place of a narrow bandpass filter, a generalized filter having an output coupled directly with a comparator would achieve the identical functional purpose were the comparator also fed a frequency reference or source. Another example would be a resonator circuit.

[0024] Coupled to bandpass filter 55 is an envelope detector 60. Upon receiving the RF bandpass output from filter 55, envelope detector 60 demodulates the RF bandpass output into a first Base Band (“BB”) signal. Envelope detector 60 achieves this objective in two steps. However, it should be obvious to one of ordinary skill in the art that the functional objective of envelope detector 60 can be realized by alternate means. Initially, envelope detector 60 rectifies the RF bandpass output by means of a rectifier. Subsequently, a low pass filter is employed for filtering the rectified RF bandpass output and forming the first BB signal.

[0025] Once the frequency of the wake up signal has been detected, the present invention employs a data rate detector for detecting the rate of data transmission of the incoming signal, which thereby rejects out of data rate signals. As such, this design employs two means for assessing two characteristics of the incoming signal. Thus, by this approach, noise and/or other sources will not falsely trigger the master receiver into waking up.

[0026] The data rate detector can be realized by a second bandpass filter 70 having a second bandwidth and a second BB signal as its output. To avert the detection of noise as a wake up signal, the second bandwidth of bandpass filter 55 is substantially narrow bandwidth. In one embodiment of the present invention, the second bandwidth is substantially narrower than the first bandwidth of the first bandpass filter. However, in the preferred embodiment, the second bandwidth need only detect a singular frequency without any harmonics.

[0027] While the present invention utilizes the herein described means for data rate detection, it should be obvious to one of ordinary skill in the art that the data rate detector can be realized using alternate hardware. For example, a comparator scheme or resonator circuit could be employed. Further, digital circuitry could also be used to accomplish the same purpose as the data detector described herein.

[0028] Further, coupled with second bandpass filter 70 is a second envelope detector 75. In order to detect the data rate of incoming signal and ascertain whether it is the wake up signal, second envelope detector 75 generates an output signal corresponding to BB signal input received from second bandpass filter 70 by demodulating the BB signal input. Second envelope detector 75 achieves this objective in two steps. However, it should be obvious to one of ordinary skill in the art that the functional objective of second envelope detector 75 can be realized by alternate means. Initially, envelope detector 75 rectifies the BB input signal second bandpass filter 70 by means of a rectifier. Subsequently, a low pass filter is employed for filtering the rectified BB signal input. As a result of this architecture, second envelope detector 75 generates a upward ramped step or a downward ramped step output signal.

[0029] Coupled to second envelope detector 75 is a comparator 80. Comparator 80 is employed to compare the output signal of second envelope detector 75 with a voltage reference. By this arrangement, comparator 80 triggers a internal wake up₁ signal. Wake up₁ signal is subsequently fed into control logic 85, which is coupled with a data processor 90, for waking up the master receiver 25.

[0030] In an alternate embodiment of the present invention, a second data rate detector is utilized. Second data rate detector, being coupled to the frequency detector, receives the first BB signal generated by the first envelope detector 60. The second data rate detector can be designed in an identical fashion as the first data detector described herein.

[0031] By this arrangement, comparator 80 triggers a internal wake UP₂ signal which is input into control logic 85, which is coupled with a data processor 90, for waking up the master receiver 25. By employing two data rate detectors, the wake up receiver can switch the data rate to be detected from the wake up signal. Here, switching logic 85 in combination with data processor 90 recognize the data rate to be detected from the wake up signal. Subsequently, when a change is necessary, a second data rate is selected as being the data rate to be detected from the wake up signal for the purposes of waking master receiver 25.

[0032] Moreover, this two data rate detector scheme can also be employed for the purpose of enabling the wake up receiver to switch modes of operation—ie., sleep mode and active mode—as described hereinabove. Thus, when a first data rate is received, master receiver 25 is to be woken in to active mode, while master receiver 25 is to be put into sleep mode when a second data rate is received.

[0033] In a further alternate embodiment of the present invention, a mixer 65 is employed. Mixer 65 is coupled between first envelope detector 60 and second bandpass filter 70. Mixer 65 is used to provide a means for frequency translating the RF bandpass output. The extent of the translation performed by mixer 65 corresponds to the local oscillator. The local oscillator, having a clock rate of f₁, provides a reference oscillating signal to the mixer 65.

[0034] Referring to FIG. 4, an alternate embodiment of the present invention is illustrated. The architecture disclosed here is further development of an alternate embodiment of FIG. 3. Here, three data rate detectors are employed. Third data rate detector, being coupled to the frequency detector, receives the first BB signal generated by a first envelope detector 110. The third data rate detector can be designed in an identical fashion as the first and second data detectors described herein.

[0035] By this arrangement, comparator 130 triggers a internal wake up_(x) signal which is input into control logic 135, which is coupled with a data processor 140, for waking up the master receiver 25. By employing three data rate detectors, the wake up receiver can switch the data rate to be detected from the wake up signal. Here, switching logic 135 in combination with data processor 140 recognize the data rate to be detected from the wake up signal. Subsequently, when a change is necessary, a third data rate is selected as being the data rate to be detected from the wake up signal for the purposes of waking master receiver 25.

[0036] In still another embodiment of the present invention, a modulation detector (not shown) is further incorporate for detecting a modulation scheme. In this embodiment, the wake up signal must also comprise a modulation format or formats. As such, the modulation detector can detect a modulation scheme selected from the group including at least amplitude modulation, frequency modulation, amplitude shift key modulation, phase shift key modulation, frequency shift key modulation, and multiphase frequency shift key modulation. The modulation detector can be realized by a variety of designs known to one of ordinary skill in the art. Thus, upon receiving the wake up signal, the modulation detector detects the format of the wake up signal and responds accordingly.

[0037] While the particular invention has been described with reference to illustrative embodiments, this description is not meant to be construed in a limiting sense. It is understood that although the present invention has been described in a preferred embodiment, various modifications of the illustrative embodiments, as well as additional embodiments of the invention, will be apparent to persons skilled in the art upon reference to this description without departing from the spirit of the invention, as recited in the claims appended hereto. For example, it should be obvious to one of ordinary skill in the art that either or both first and second communications devices, such as transmitter 10 and a receiver 25, can further comprise transceiver properties for the purposes of the present invention. It is therefore contemplated that the appended claims will cover any such modifications or embodiments as fall within the true scope of the invention.

[0038] All of the U.S. Patents cited herein are hereby incorporated by reference as if set forth in their entirety. 

What is claimed is:
 1. A communications system, comprising: a) a first communications device for receiving data and a wake up signal, comprising: i. active mode of operation and a sleep mode of operation for reducing power consumption; and ii. means for switching said first communications device between said active mode and said sleep mode, said switching means being responsive to said wake up signal; and b) a second communications device for transmitting said data to said first device during said active mode and transmitting said wake up signal to said first device during said sleep mode.
 2. A communications system, according to claim 1 , wherein said switching means comprises: a) a substantially low power receiver for receiving said wake up signal; and b) means for comparing a characteristic of said wake up signal with a reference.
 3. A communications system, according to claim 2 , wherein said comparing means comprises a frequency detector.
 4. A communications system, according to claim 3 , wherein said comparing means comprises a rate of data transmission detector.
 5. A communications system, according to claim 4 , wherein said comparing means comprises a modulation scheme detector.
 6. A communications system, according to claim 1 , wherein said first and second devices comprise at least one of a receiver and a transmitter.
 7. A communications system having reduced power consumption, comprising: a) a master receiver for receiving data, said master receiver comprising: i. at least a first and a second mode of operation, said second mode using substantially less power than said first mode; ii. a substantially low power receiver for receiving a wake up signal, said wake up signal having a predetermined frequency and at least a first rate of data transmission, said low power receiver comprising: (1) means for detecting a characteristic of said wake up signal; and (2) a switch for switching between at least said first and said second modes in response to said detecting means; and b) a transmitter for transmitting data to said master receiver during said first mode and for transmitting said wake up signal to said low power receiver during said second mode.
 8. A communications system, according to claim 7 , wherein said detecting means comprises a frequency detector for detecting said frequency of said wake up signal.
 9. A communications system, according to claim 8 , wherein said frequency detector comprises: a) a frequency source; and b) a comparator for comparing said wake up signal with said frequency source.
 10. A communications system, according to claim 8 , wherein said frequency detector comprises: a bandpass filter having a bandpass output.
 11. A communications system, according to claim 10 , further comprising an envelope detector coupled to said bandpass filter, said envelope detector comprising: a) a rectifier for rectifying said bandpass output; and b) a low pass filter for filtering said rectified bandpass output.
 12. A communications system, according to claim 8 , wherein said detecting means comprises a data rate detector for detecting said first rate of data transmission of said wake up signal, said data rate detector being coupled with said frequency detector and having an output.
 13. A communications system, according to claim 8 , wherein said wake up signal further comprises at least a second rate of data transmission, said at least a first and second rate of data transmission corresponds with said at least a first and second mode of operation, said detecting means comprises a data rate detector for detecting said at least a first and second rate of data transmission of said wake up signal, said data rate detector being coupled with said frequency detector and having an output.
 14. A communications system, according to claim 12 , wherein said data rate detector comprises: a bandpass filter having a bandpass output.
 15. A communications system, according to claim 14 , further comprising an envelope detector coupled to said second bandpass filter, said envelope detector comprising: a) a rectifier for rectifying said bandpass output; and b) a low pass filter for filtering said rectified bandpass output.
 16. A communications system, according to claim 15 , wherein said data rate detector further comprises: a divider for frequency dividing said rectified bandpass output by a predetermined number, said divider being coupled with said bandpass signal to said divider, said number being responsive to said reference oscillating signal.
 17. A communications system, according to claim 12 , wherein said detecting means further comprises a comparator for comparing an output of said data rate detector with a reference voltage, thereby enabling said switch when said frequency detector detects said frequency of said wake up signal and said data rate detector detects said data rate of said wake up signal.
 18. A communications system, according to claim 12 , wherein said detecting means comprises a modulation scheme detector.
 19. A communications system, according to claim 18 , wherein said modulation scheme is selected from the group including at least amplitude modulation, frequency modulation, amplitude shift key modulation, phase shift key modulation, frequency shift key modulation, and multiphase frequency shift key modulation.
 20. A communications system for use in an identification system having reduced power consumption, comprising: a) a master receiver for receiving data having at least an active mode and a sleep mode of operation; b) a transmitter for transmitting data to said master receiver during said active mode and for transmitting a wake up signal during said sleep mode, said wake up signal having a predetermined frequency and rate of data transmission; and c) a switch for switching said master receiver between said active mode and said sleep mode, said switch comprising a wake up receiver for receiving said wake up signal, said switch being enabled in response to said wake up signal, said wake up receiver using substantially less power than said master receiver, said wake up receiver comprising: i. a frequency detector for detecting said frequency of said wake up signal, said frequency detector comprising: (1) a first bandpass filter having a first bandwidth, said first bandwidth being substantially narrow; and (2) a first envelope detector coupled to said first bandpass filter; ii. a data rate detector for detecting said rate of data transmission of said wake up signal, said data rate detector having an output and comprising: (1) a second bandpass filter having a second bandwidth, said second bandwidth being substantially narrow; and (2) a second envelope detector coupled to said second bandpass filter; and iii. a comparator for comparing said output of said data rate detector with a reference voltage, thereby enabling said switch when said frequency detector detects said frequency of said wake up signal and said data rate detector detects said data rate of transmission of said wake up signal.
 21. A communications system for use in an identification system having reduced power consumption, according to claim 20 , wherein said second bandwidth is substantially narrower than said first bandwidth.
 22. A communications system for use in an identification system having reduced power consumption, according to claim 20 , wherein said switch and said master receiver are positioned on a radio frequency identification tag.
 23. A method for reducing the consumption of energy in operating a communications system, said communications system comprising a transmitter, a master receiver and a wake up receiver, said master receiver having at least an active mode and a sleep mode of operation, said wake up receiver using substantially less power than said master receiver, comprising the steps of: transmitting data to said master receiver during said active mode and a wake up signal to said wake up receiver during said sleep mode, said wake up signal having a predetermined frequency, and a predetermined rate of data transmission; detecting said wake up signal; and enabling up said master receiver in response to said detecting.
 24. A method for reducing the consumption of energy in operating a communications system, according to claim 23 , wherein said detecting comprises the steps of: detecting said predetermined frequency of said wake up signal; and detecting said predetermined data rate of said wake up signal; and generating an output upon detecting said predetermined frequency and said predetermined data rate.
 25. A method for reducing the consumption of energy in operating a communications system, according to claim 24 , wherein said generating an output comprises the step of: comparing said output with a reference voltage, thereby generating an enabling signal to said switch upon detecting said predetermined frequency and said predetermined data rate.
 26. A method for reducing the consumption of energy in operating a communications system, according to claim 24 , wherein said wake up signal comprises a predetermined modulation scheme, said modulation scheme being at least one of amplitude shift keying, frequency shift keying, phase shift keying and amplitude shift keying and said detecting further comprises the step of: detecting said predetermined modulation scheme. 